Important Questions for Class 10 Science Chapter 1 – Chemical Reactions And Equations

# Important Questions for Class 10 Science Chapter 1 – Chemical Reactions And Equations

When the bonds between reactant molecules are broken and new bonds are formed between product molecules, a chemical reaction occurs, resulting in the formation of a new substance. A chemical equation is simply a mathematical statement that represents the formation of a product from reactants. The number of atoms for each element in a chemical reaction must be the same on the reactant and product sides in order for the equation to be balanced. In this article. explore Important Questions for Class 10 Science Chapter 1 – Chemical Reactions And Equations.

Students should pay attention to the following important topics from Chemical Reactions And Equations:

• How to write a chemical equation
• Equilibrium in chemical equations
• Symbols for the representation of physical states
• Reactions of chemical types
• The displacement reaction
• What the effects of oxidation reactions are in everyday life

## Class 10 Science Important Questions Chapter 1 – Chemical Reactions and Equations

Q1. (a) State the law that is followed by balancing a chemical equation.

(b) Balance the following chemical equation: Na + H3O → NaOH + H2

Solution:

(a) Law of conservation of mass is followed for balancing a chemical equation which states that mass can neither be created nor destroyed in a chemical reaction. That is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants in a balanced equation.

(b) 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Q2. (a) State the law that is followed by balancing a chemical equation.

(b) Balance the following chemical equation: Na + H3O → NaOH + H2

Solution:

(a) Law of conservation of mass is followed for balancing a chemical equation which states that mass can neither be created nor destroyed in a chemical reaction. That is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants in a balanced equation.

(b) 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Q3. In which of the following, the identity of the initial substance remains unchanged?

(a) Curdling of milk

(b) Formation of crystals by process of crystallisation

(c) Fermentation of grapes

(d) Digestion of food

Solution:

(b): Formation of crystals is a physical change rest others are chemical change.

Q4. State the type of chemical reactions, represented by the following equations

(a) A + BC → AC + B

(b) A + B → C

(c) PQ + RS → PS + RQ

(d) A2O3 + 2B → B2O3 + 2A

Solution:

(a) Displacement reaction.

(b) Combination reaction.

(c) Double displacement reaction.

(d) Displacement reaction or redox reaction.

Q5. Take 3 g of barium hydroxide in a test tube, now add about 2 g of ammonium chloride and mix the contents with the help of a glass rod. Now touch the test tube from outside.

(i) What do you feel when touching the test tube?

(ii) State the inference about the type of reaction occurred.

(iii) Write the balanced chemical equation of the reaction involved.

Solution:

(i) When barium hydroxide is added into ammonium chloride, the bottom of test tube is found to be cooler.

(ii) It is an endothermic reaction.

(iii) Ba(OH)2 + 2NH4Cl → BaCl2 + 2NH4OH

Q6. (a) Can a displacement reaction be a redox reaction? Explain with the help of an example.

(b) Write the type of chemical reaction in the following:

(i) Reaction between an acid and a base

(ii) Rusting of iron.

Solution:

(a) Consider the following displacement reaction:

Zn(s)+ CuSO4(aq) → ZnSO4(aq) + Cu(s)

Here, Zn has changed into ZnSO4 (i.e., Zn2+ ions) by loss of electrons. Hence, Zn has been oxidised. CuSO4 (i.e., Cu2+) has changed into Cu by gain of electrons. Hence, CuSO4 has been reduced. Thus, the above reaction is a displacement reaction as well as a redox reaction.

(b) (i) Neutralisation reaction

(ii) Oxidation reaction.

Q7. What happens when food materials containing fats and oils are left for a long time? List two observable changes and suggest three ways by which this phenomenon can be prevented.

Solution:

Food materials containing fats and oils change their taste and smell due to a process called rancidity. Rancidity is a process in which air reacts with fats and oils which changes the smell and taste of food.

Methods of prevention:

Vacuum packing,

refrigeration of food materials,

placing of food materials, away from direct sunlight.

Q8. (a) Define a balanced chemical equation. Why should an equation be balanced?

(b) Write the balanced chemical equation for the following reaction:

(i) Phosphorus burns in presence of chlorine to form phosphorus penta chloride.

(ii) Burning of natural gas.

(iii) The process of respiration.

Solution:

(a) Balanced chemical equation has an equal number of atoms of different elements in the reactants and products. According to law of conservation of mass, matter can neither be created nor be destroyed in a chemical reaction.

(b)(i) P4 (s) + 10Cl2 (g) ———> 4PCl5 (S)

(i)CH4 (g) + 2O2 (g) ———> CO2 (g) + 2H2O(l) + heat energy

(iii) C6H12O6 (s) + 6O2 (g) + 6H2O ———> 6CO2 (aq) + 12H2O (l) + energy

Q9. (a) Explain two ways by which food industries prevent rancidity.

(b) Discuss the importance of decomposition reactions in the metal industry with three points.

Solution:

(a) (i) Rancidity can be prevented by adding antioxidants to food containing

fat and oil, e.g. butylated hydroxy anisole is added to butter as an antioxidant.

(ii) It can be prevented by packaging fat and oil containing foods in nitrogen gas.

(b) (i) Molten NaCl is electrolytically decomposed to form sodium metal.

(ii) Aluminium metal is obtained by electric decomposition of bauxite ore mixed with cryolite.

(iii) Carbonate ores are thermally decomposed to give metal oxide which on reduction give metal.

Q10. Write the balanced chemical equations for the following reactions and identify the type of

reaction in each case.

(a ) In the thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.

(b ) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.

(c ) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium

chloride solution and solid iodine.

(d ) Ethanol is burnt in the air to form carbon dioxide and water and releases heat.

Solution:

(a ) Fe2O3 (s) + 2 Al (s) → Al2O3 (s) + 2 Fe (l) + Heat

It is a displacement or redox reaction.

(b ) 3 Mg (s) + N2 (g) → Mg3N2 (s)

It is a combination reaction.

(c ) 2 KI (aq) + Cl2 (g) → 2 KCl (aq) + I2 (s)